β-Phase formation in poly(9,9-di-n-octylfluorene) by incorporating an ambipolar unit containing phenothiazine and 4-(dicyanomethylene)-2-methyl-6-[p- (dimethylamino)styryl]-4H-pyran

Article abstract of DOI:10.1039/b909300a

Novel fluorene-based blue-light-emitting copolymers (F8Rs) in the β-phase are designed and synthesized using the palladium-catalyzed Suzuki reaction. The β-phase can be generated by introducing an ambipolar unit, that contains 10-n-hexylphenothiazine (PTZ

Full text of DOI:10.1039/b909300a

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www.rsc.org/materials | Journal of Materials Chemistry
b-Phase formation in poly(9,9-di-n-octylfluorene) by incorporating an
ambipolar unit containing phenothiazine and 4-(dicyanomethylene)-2-methyl-
6-[p-(dimethylamino)styryl]-4H-pyran†
Sang Kyu Lee,a Taek Ahn,b Jong-Hwa Park,c Young Kwan Jung,d Dae-Sung Chung,e Chan Eon Parke
c
*
and Hong Ku Shim
Received 11th May 2009, Accepted 24th July 2009
First published as an Advance Article on the web 18th August 2009
DOI: 10.1039/b909300a
Novel fluorene-based blue-light-emitting copolymers (F8Rs) in the b-phase are designed and
synthesized using the palladium-catalyzed Suzuki reaction. The b-phase can be generated by
introducing an ambipolar unit, that contains 10-n-hexylphenothiazine (PTZ) and
4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM) (as the donor and
acceptor moieties, respectively) on a polyfluorene backbone. By comparing the absorption (peak at
437 ꢀ 1 nm), photoluminescence (PL) (peak at 441 ꢀ 1 nm), and X-ray diffraction (XRD) (peak
centered around 2q ¼ 7.0ꢁ) characteristics of the resulting polymers (F8Rs) with those of the
polyfluorene homopolymer (PFO), we found that fluorene-based copolymers with ambipolar
moieties, such as PTZ and DCM, can prompt the formation of the b-phase after spin-coating without
gelling in a poor solvent, exposure to tetrahydrofuran vapor, cooling to liquid-N2 temperature, and
reheating. The PL and electroluminescence (EL) efficiencies of the copolymer F8R5 are higher
than those of PFO (by factors of two and 15, respectively). The EL spectrum of the copolymer showed
almost pure blue emission, with CIE (Commission Internationale de l0Eclairage) coordinates of
x ¼ 0.17 and y ¼ 0.10.
In addition to PLEDs applications, PFO has also been inves-
Introduction
tigated in terms of its morphological phases. A well-studied
example is the b-phase, which is a phase with a planar zigzag
conformation resulting in an extended conjugation length.2,6–11
Whitehead et al.7a reported that the generation of the b-phase for
a PFO thin film usually requires exposure to solvent vapors7 or
thermal treatments after spin-coating (e.g., cooling to liquid-
nitrogen temperature and subsequent reheating to room temper-
ature).8 Also, the generation of the b-phase needs to be processed
from its solution in a solvent with low solvent power or by addi-
tion of a poor solvent.9 Bazan et al.6a reported that the incorpo-
ration into the casting solvent of high-boiling-point additives as
poor solvents for PFO can lead to high b-phase contents within
the spun films. A few volume percent of 1,8-diiodooctane (DIO)
added to the o-xylene medium used to dissolve PFO allows the
b-phase content to be tailored between 0 and 45%. The formation
of the b-phase of PFO is evidenced by the presence of an
absorption peak at 437 ꢀ 1 nm, a PL peak at 441 ꢀ 1 nm, and an
X-ray diffraction (XRD) peak centered around 2q ¼ 7.0ꢁ.2,6–11
Although many studies on the b-phase of polyfluorene
homopolymers have been conducted,6–11 there are no investiga-
tions so far on the effect of incorporating ambipolar moieties
into the PF backbone of the b-phase of a fluorene-based copol-
ymer (without thermal treatment or the addition of a poor
solvent) on the generation and behavior of PLEDs.
Conjugated polymers have attracted much attention as active
materials for organic electronic devices, such as light-emitting
diodes (LEDs),1–3 field-effect transistors (FETs),4 and photo-
voltaic cells.5 In particular, interest in polymeric light-emitting
diodes (PLEDs) has increased because PLEDs are well-suited for
flat-panel displays. This is due to their good processability, low
operating voltage, fast response time, and facile color tunability
over the full visible range. Among all the known p-conjugated
polymers, poly(9,9-di-n-octylfluorene) (PFO) is the most prom-
ising candidate as a blue-light-emitting polymer because of its
highly efficient photoluminescence (PL), good thermal, chemical,
and electrochemical stability, and convenient solubility in
common organic solvents.2,3
aEnergy Materials Research Center, Korea Research Institute of Chemical
Technology (KRICT), 100 Jang-dong, Yuseong-gu, Dae-jeon, 305-600,
Korea
bInformation and Electronics Polymer Research Center, Korea Research
Institute of Chemical Technology (KRICT), 100 Jang-dong, Yuseong-gu,
Dae-jeon, 305-600, Korea
cDepartment of Chemistry and School of Molecular Science (BK 21),
Korea Advanced Institute of Science and Technology, 373-1 Guseong-
dong, Yuseong-gu, Dae-jeon, 305-701, Korea. E-mail: hkshim@kaist.ac.
kr; Fax: +82-42-350-2810; Tel: +82-42-350-2827
dOLED Technology Development Team3, LG Display Co., 191-1,
Gongdan-dong, Gumi-si, Gyungsangbuk-do, 730-030, Korea
ePolymer Research Institute, Department of Chemical Engineering,
Pohang University of Science and Technology, Pohang, 790-784, Korea
† Electronic supplementary information (ESI) available: Detailed UV
and PL spectra data. See DOI: 10.1039/b909300a
In this article, we report a novel strategy to improve both the
color purity in the blue emission and the electroluminescence (EL)
device efficiency by incorporating an ambipolar unit that contains
10-n-hexylphenothiazine (PTZ) and 4-(dicyanomethylene)-
2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM) as the
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donor and acceptor moieties, respectively. This procedure leads to
the formation of a long conjugated species (regarded as the
b-phase), on the PF backbone. Interestingly, the PL efficiency and
EL device efficiency of the fluorene copolymers (F8Rs) containing
the ambipolar unit are higher than those of the PF homopolymer
(by factors of two and 15, respectively). The EL spectrum of
the copolymer showed an almost pure blue emission, with CIE
(Commission Internationale de l0Eclairage) coordinates of
x ¼ 0.17 and y ¼ 0.10 (within the limit for pure blue emission
x + y < 0.302a), and remained stable at different driving voltages.
3-carbaldehyde, according to the Vilsmeier reaction.12 Then, the
product 1 was brominated with n-bromosuccinimide (NBS) to
obtain the product 2, which was further treated to yield the key
monomer bis-PTZDCM (3)—afforded by Knoevenagel
condensation13 with (2,6-dimethyl-4H-pyran-4-ylidene)malono-
nitrile (in 68% yield). Finally, the F8Rs were synthesized via the
Suzuki reaction. To find the optimized composition of the
ambipolar monomers for obtaining high efficiency and pure
blue-light emission (without shifts in the emission color), we
investigated a series of three polymers containing 0.05, 0.08, and
0.10 mol% ambipolar monomers, denoted as F8R5, F8R8, and
F8R10, respectively. The F8Rs synthesized in this work were
readily soluble in common organic solvents, such as THF,
chloroform, and toluene. Their molecular weights were measured
by gel-permeation chromatography using THF as the eluent. The
number-average molecular weights (Mn) of the copolymers were
found to be in the range of 63 000–123 000, with polydispersity
Results and discussion
Synthesis and characterization of the polymers
As shown in Scheme 1, the new F8Rs were synthesized following
a four-step process. The compound 10-n-hexylphenothiazine was
used as starting material to prepare 10-n-hexylphenothiazine-
Scheme 1 Synthetic scheme for the monomer and copolymers.
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Table 1 Physical properties of the polymers
Ratio (fluorene : bis-PTZDCM)
In the feed composition
Polymer
Mn[kg/mol]
PDI
In the copolymersa
Yield(%)
Tg(ꢁC)
T5d(ꢁC)b
F8R5
F8R8
F8R10
100
63
123
1.9
2.2
2.3
99.95 : 0.05
99.92 : 0.08
99.90 : 0.10
99.87 : 0.13
99.85 : 0.15
99.80 : 0.20
75
65
68
63
62
64
418
415
416
a
Calculated from elemental analysis data. b Temperature resulting in 5% weight loss based on initial weight.
Fig. 2 UV-vis absorption and PL spectra of the copolymers in
chloroform.
Fig. 1 DSC heating traces. DSC cooling traces showing crystallization
at rather low temperature near 100 ꢁC at a cooling rate of 10 ꢁC/min and
subsequent transformation into the a-phase that melts near 160 ꢁC.
wavelength and spectral pattern as well as the PL spectra of the
polymers are not significantly different from those of PFO.
Fig. 3 shows UV-vis absorption and PL emission spectra of
thin films of the polymers. Thin films of the F8Rs were prepared
from chlorobenzene solution (c ¼ 10 mg/mL) by spin-coating on
a quartz substrate for 60 s at 1500 rpm. The F8Rs show an
absorption maximum at about 395 nm, which is attributed to
a p–p* transition of the polymer. Also, a new peak appears at
436 nm whose intensity increases upon increasing the fraction of
DCM units but without any shift in position. The fact that this
emerging peak does not shift in position indicates that the
incorporation of the ambipolar unit results in very long and
indices (PDIs) in the range: 1.9–2.3. The synthesized copolymers
1
were successfully characterized by H NMR spectroscopy and
elemental analysis. The actual molar ratio of fluorene/
bis-PTZDCM in the copolymers was calculated using elemental
analysis. The nitrogen contents in the copolymers were calcu-
lated and found to be very close to the feed ratios, as listed in
Table 1. The polymers exhibited glass transition temperatures
(Tg) ranging from 62 to 64 ꢁC—determined using differential
scanning calorimetry (DSC) at a rate of 10 ꢁC/min under
a nitrogen atmosphere. Chen et al. reported that b phase is
generally metastable, which transforms into crystalline (a0 and a)
phases upon subsequent increases in temperature before final
melting of crystalline order into nematic melt near 160 ꢁC.2b,c It is
supported by the presence of the endothermic shoulder near
140 ꢁC before the final melting at 160 ꢁC in the DSC heating trace
as shown in Fig. 1.
All the copolymers had very good thermal stabilities, losing
ꢁ
less than 5% of their weight upon heating to about 415 C. The
physical properties of the polymers are summarized in Table 1.
Optical properties
Normalized UV-vis absorption and PL emission spectra of the
polymers in chloroform solutions are shown in Fig. 2. All the
polymers exhibit absorption maxima at about 390 nm, which is
almost consistent with the absorption peak for PFO homopol-
ymer. It suggests that most of the absorption was caused by the
fluorene units. As shown in Fig. 2, the maximum absorption
Fig.
3 UV-vis absorption and PL spectra of thin films of the
copolymers.
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extended chain segments (i.e., the b-phase) without the formation
of intermediate states.6 We found that the F8Rs with ambipolar
units can prompt the formation of the b-phase after spin-coating
without the need for further thermal treatment (this is evidenced
by the presence of an absorption peak at 436 nm in addition to
the main absorption peak at 395 nm).
As shown in Fig. 3, the PL spectra of amorphous PFO exhibit
emission peaks at 422 (0–0 band), 446 (0–1 band), and 476 nm
(0–2 band). On the other hand, the PL spectra of the F8Rs
(excited at the main absorption wavelength of 395 nm) show
characteristic bands attributed to the b-phase, at 440 (0–0 band),
465 (0–1 band), and 498 nm (0–2 band), as well as an additional
0–0 band from the amorphous matrix at 424 nm. This result
indicates that parts of the chains undergo an extension of the
conjugating length (b-phase) upon incorporating the ambipolar
unit into the PF polymer system. In addition, the presence of an
emission band at 424 nm in the PL spectrum indicates a partial
energy transfer from the amorphous phase to the b-phase, which
acts as a self-dopant.2a These phenomena in UV and PL spectra
are also shown for the polymers with other ratios of the ambi-
polar monomers (see ESI†).
Fig. 4 Out-of-plane X-ray scattering patterns of the F8R copolymers.
centered at 2q ¼ 21ꢁ, which indicates that the films are amor-
phous collections of randomly oriented polymer chains. The
XRD profiles of F8Rs also show these broad halos, but they also
exhibit an additional peak, which is centered at around 2q ¼ 7.0ꢁ
and is characteristic of the b-phase.
Upon increasing the fraction of the DCM units from F8R5 or
F8R8 to F8R10, we observe an increase in the intensity of an
additional peak which appears at 606 nm. This peak at 606 nm is
attributed to the DCM segments. The blue and orange emission
bands observed in the PL spectrum of F8R10 result from
a partial energy transfer from the fluorene segments to the DCM
segments.
Electrochemical properties
The electrochemical properties of the polymers were studied to
investigate the redox behavior, and to determine the energy levels
of their highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO). The electrochemical
processes probed by cyclic voltammetry (CV) are similar to those
involved in charge injection and transport processes in LED
devices. Cyclic voltammetry was used to investigate the electro-
chemical properties of the resulting copolymers in an electrolyte
consisting of a 0.1 M tetrabutylammonium hexafluorophosphate
(n-Bu4NPF6) solution in acetonitrile. All measurements were
calibrated using ferrocene (Fc) as a standard.14 The copolymer
films were prepared by dip-coating a Pt electrode into the poly-
mer solution (10 mg in 3 ml of chloroform) and drying the
resulting film in air. In the anodic scan, the onset of oxidation of
PFO, F8R5, F8R8, and F8R10 was found to occur at 1.41, 1.33,
1.35, and 1.37 V (vs. SCE), respectively, corresponding to the
ionization potential (Ip) values of ꢂ5.80, ꢂ5.72, ꢂ5.74, and
ꢂ5.76 eV, respectively, according to the empirical relationship
proposed by de Leeuw et al. [Ip (HOMO) ¼ ꢂ(Eonset,ox + 4.39)
(eV), where Eonset,ox is the onset potential of oxidation].15
Unfortunately, it was difficult to obtain the LUMO energies for
The relative fluorescence quantum yields (Ffl) of F8R films
were estimated by comparison with the fluorescence intensity of
a PFO thin-film sample. In the film state, the value of Ffl for
F8R5 is twice as high as that of PFO. The increased PL efficiency
is closely related to an improvement in the overall external
quantum efficiency of the LED devices. Table 2 lists all the
UV-vis absorption and PL emission maxima of the polymers,
together with their PL quantum efficiencies.
X-Ray diffraction analysis
The formation of the b-phase is also supported by the presence
of a characteristic peak corresponding to this phase in the
XRD pattern. Synchrotron X-ray diffraction analyses of the
polymers films were performed at the 10C1 beam line (wave-
˚
length z 1.54 A) of the Pohang Accelerator Laboratory (PAL).
Fig. 4 shows the out-of-plane X-ray scattering patterns for PFO
and F8Rs. The XRD profile of PFO exhibits a broad halo
Table 2 Spectral data, energy levels, and EL characteristics of the polymers
Solution, lmax (nm)
Film, lmax (nm)
Absorption
Emission
Absorption
Emission
HOMO/LUMO (eV)b
CIE (x, y)c
a
Ffl
PFO
382
390
390
390
415, 437, 469
417, 441, 472
417, 441, 472
417, 441, 472
384
395
395
395
422, 446, 476
424, 440, 465
424, 440, 465
424, 440, 606
1.00
1.93
1.58
1.02
ꢂ5.80/ꢂ2.87
ꢂ5.72/ꢂ2.81
ꢂ5.74/ꢂ2.81
ꢂ5.76/ꢂ2.81
(0.20, 0.16)
(0.17, 0.10)
(0.19, 0.14)
(0.32, 0.20)
F8R5
F8R8
F8R10
a
b
Film fluorescence quantum yields estimated by comparison with the fluorescence intensity of the PFO polymer. Calculated from the empirical
equation: Ip(HOMO) ¼ ꢂ(Eonset,ox + 4.39) (eV). c Determined from the EL spectra at 8 V.
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the copolymers using this technique, so these values were esti-
mated from the optical band gaps (taken as the absorption onsets
of the UV-vis spectra for the polymer films) and the HOMO
energies. The energies of the LUMO levels of PFO, F8R5, F8R8,
and F8R10 are listed in Table 2. Using this approach, we
estimated the energy band gaps of PFO, F8R5, F8R8, and
F8R10 to be 2.87, 2.81, 2.81, and 2.81 eV, respectively.
Electroluminescence properties and current-voltage-luminance
(I-V-L) characteristics
To investigate the EL properties of the polymers, we fabricated
devices with the configuration: ITO/PEDOT:PSS (50 nm)/F8Rs
(80 nm)/Ca (50 nm)/Al (100 nm) and characterized them as
a function of the applied voltage. The EL spectra and current-
voltage-luminance (I-V-L) characteristics were measured under
ambient conditions. The F8R copolymer was spin-coated from
a 1.0 wt% solution in chlorobenzene onto a PEDOT-coated ITO
substrate. The EL spectra of the devices at 8 V are shown in
Fig. 5. As can be seen, the EL spectra of the polymers are almost
identical to the PL spectra of the spin-coated films, which indi-
cates that a similar energy-transfer process is involved in both
cases.
Fig.
6
EL spectra of the F8R5 devices with the configuration:
ITO/PEDOT:PSS/polymer/Ca/Al at various driving voltages.
The CIE coordinates of the F8R devices at a driving voltage of
8 V are shown in the inset of Fig. 5. Interestingly, the color
coordinates of F8R5 (0.17, 0.10) are close to those of the stan-
dard blue emission (0.14, 0.08). This high purity in blue emission
is due to the weaker intensity in the long-wavelength region
relative to the EL spectrum for PFO.
Blue-emitting devices fabricated using the resulting polymer
show a very good current stability. Fig. 6 compares the EL
spectra of devices fabricated with the F8R5 copolymer at
different operating voltages. The CIE coordinates show no
significant changes, namely, (0.17, 0.10), (0.17, 0.11), (0.18, 0.11),
and (0.18, 0.12) at driving voltages of 8, 9, 10, and 11 V,
respectively.
Fig. 7 shows the voltage-luminance and voltage-current effi-
ciency characteristics of the devices. The units fabricated with the
F8Rs showed a turn-on voltage in the range of 4.8–5.6 V, which
is quite similar to the turn-on voltage of PFO (namely, 5.2 V).
Fig. 7 (a) Voltage vs. current efficiency and (b) voltage vs. brightness
characteristics of EL devices based on the F8R copolymers.
Moreover, as shown in Fig. 7, the F8Rs exhibit apparently higher
EL efficiencies. In particular, the maximum current efficiency
obtained for F8R5 was 0.74 cd/A, which is 15 times higher than
that measured for PFO (i.e., 0.05 cd/A). Moreover, the maximum
luminance of F8R5 for bright blue emission was found to be
1900 cd/m2 (at a bias of 8.8 V and a current density of
380 mA/cm2)—a value that is also much higher than that of PFO
(namely, 120 cd/m2 at a bias of 9.2 V and a current density of
460 mA/cm2).
Fig. 5 EL spectra of copolymer devices with the configuration: ITO/
PEDOT:PSS/polymer/Ca/Al at 8 V. Inset: CIE coordinates (x, y) of the
PFO, F8R5, F8R8, and F8R10 devices at 8 V (HDTV ¼ dashed line).
7066 | J. Mater. Chem., 2009, 19, 7062–7069
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solution, dimethylformamide (DMF), (2,6-dimethyl-4H-pyran-
4-ylidene)malononitrile, piperidine, n-propanol, phenylboronic
acid, and toluene (99.8%, anhydrous) were purchased from
Aldrich. Palladium(II) acetate was purchased from Strem
Chemicals Co. Chloroform and bromobenzene were purchased
from Junsei Chemical Co. All chemicals were used without further
purification. The monomers 2,7-dibromo-9,9-di-n-octylfluo-
rene and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,
9-di-n-octylfluorene and the polymer poly(9,9-di-n-octylfluorene)
(PFO) were prepared according to reported procedures. The
number-average molecular weight (Mn) of PFO, as determined
with gel permeation chromatography using a polystyrene
standard, was found to be 12 000, with a polydispersity index
(PDI) of 2.3.
Conclusions
We have reported for the first time that new fluorene-based
copolymers containing ambipolar moieties, such as PTZ and
DCM, can prompt the formation of the b-phase along the
polymer chain. Our results are based on detailed studies of the
UV-vis absorption and PL spectra of the resulting polymers as
well as on the analysis of their XRD profiles. These analyses are
in excellent accord with previous studies on the b-phase. The EL
devices based on the b-phase PF copolymers F8R5 and F8R8
exhibited a deep blue emission which remained almost constant
upon varying the driving voltage and the EL efficiency. This deep
blue emission originates from an energy transfer from the
amorphous matrix to the b-phase and a weaker long-wavelength
tail. The EL devices based on F8R5 exhibited a greater efficiency
(0.74 cd/A) and an improved brightness (1900 cd/m2) relative to
the devices containing PFO. The approach presented herein is
a new and useful method to obtain the b-phase of a polymer.
Synthesis of 10-n-hexylphenothiazine-3-carbaldehyde (1). A
500 mL two-necked flask containing 65 mL (0.846 mol) of
anhydrous DMF was cooled in an ice-bath. To this solution,
22.3 mL (0.243 mol) of phosphorus oxychloride was added
dropwise for 30 min. 10-n-Hexylphenothiazine (20 g, 69.3 mmol)
in 60 mL of 1,1,2-trichloroethane was added to the above solu-
tion and heated to ca. 90 ꢁC for 2 days. This solution was cooled
to room temperature, poured into ice water, and neutralized to
pH 6–7 by dropwise addition of saturated aqueous sodium
hydroxide solution. The mixture was extracted with ethyl acetate
(EA)/water. The organic layer was dried with anhydrous MgSO4
and then concentrated under reduced pressure. The crude
product was purified by column chromatography with hexane/
ethyl acetate (4:1) as eluent. A bright yellow oil was obtained
Experimental
1
The synthesized compounds were characterized with H NMR
spectra obtained using a Bruker AVANCE 400 MHz Spec-
trometer. Elemental analysis was performed using an EA 1110
Fisons analyzer. UV-visible analysis was performed with a
Shimadzu Jasco V-530 UV/vis spectrometer. The number- and
weight-average molecular weights of the polymers were deter-
mined by gel permeation chromatography (GPC) on a Waters
GPC-150C instrument, using tetrahydrofuran (THF) as the
eluent and polystyrene as the standard. Thermogravimetric
analysis (TGA) and differential scanning calorimetry (DSC)
were performed under a nitrogen atmosphere at a heating rate of
1
(15.1 g, 70%). H NMR (400 MHz, DMSO-d6, ppm): d 9.77
(s, 1H), 7.70 (d, 1H), 7.54 (s, 1H), 7.20 (t, 1H), 7.12 (m, 2H), 7.03
(m, 2H), 3.89 (t, 2H), 1.79 (q, 2H), 1.43 (m, 2H), 1.28 (m, 4H)
0.85 (m, 3H). 13C NMR (100 MHz, DMSO-d6, ppm): d 190.9,
149.9, 143.0, 131.2, 130.7, 128.6, 128.4, 128.0, 124.0, 123.3, 121.1,
116.5, 115.5, 48.5, 31.2, 26.6, 26.3, 22.5, 13.9. Anal. Calcd for
C19H21NOS: C, 73.27; H, 6.80; N, 4.50; S, 10.30. Found: C,
73.15; H, 6.87; N, 4.40; S, 10.25%.
ꢁ
10 C/min with a Dupont 9900 analyzer. The thicknesses of the
polymer films were measured using an Alpha step 200 profil-
ometer. Photoluminescence (PL) spectra of the polymers were
obtained with a Spex Fluolog-3 (Model FL3-11) spectrofluo-
rometer. Electroluminescence spectra were obtained with
a Minolta CS-1000. The current-voltage (I-V) and luminescence-
voltage (L-V) characteristics of the devices were measured with
a Keithley 238 as the voltage and current source and a Minolta
LS-100 as the luminance detector. All the measurements were
performed in air at room temperature.
Synthesis of 7-bromo-10-n-hexylphenothiazine-3-carbaldehyde
A solution of 10-n-hexylphenothiazine-3-carbaldehyde
(2).
(5.7 g, 18.3 mmol), N-bromosuccinimide (3.3 g, 18.3 mmol),
acetic acid (40 ml) and toluene (10 ml), was stirred for 3 hr. This
solution was poured into water. The mixture was extracted with
EA/water. The organic layer was dried with anhydrous MgSO4
and then concentrated under reduced pressure. The crude
product was purified by column chromatography with hexane as
eluent. A bright yellow oil was obtained (5.07 g, 71%). 1H NMR
(400 MHz, DMSO-d6, ppm): d 9.78 (s, 1H), 7.64 (d, 1H), 7.54
(s, 1H), 7.23 (m, 2H), 6.87 (d, 1H), 6.68 (d, 1H), 3.82 (t, 2H), 1.78
(m, 2H), 1.41 (m, 2H), 1.27 (m, 4H) 0.86 (t, 3H). 13C NMR
(100 MHz, DMSO-d6, ppm): d 190.5, 149.6, 142.4, 131.0, 130.4,
130.2, 129.1, 127.9, 125.2, 122.9, 118.1, 115.8, 114.9, 47.0, 30.7,
25.9, 25.6, 22.0, 13.8. Anal. Calcd for C19H20BrNOS: C, 58.46;
H, 5.16; N, 3.59; S, 8.21. Found: C, 58.41; H, 5.26; N, 3.50; S,
8.09%.
Fabrication of the LED devices
In this study, the devices were fabricated with ITO/PEDOT:PSS/
polymer/Ca/Al structures. The procedure for cleaning the ITO
surface included sonication and rinsing in deionized water,
methanol, and acetone. The hole-transporting PEDOT:PSS layer
was spin-coated onto each ITO anode from a solution purchased
from Bayer Co. Each polymer solution was then spin-coated onto
the PEDOT:PSS layer. The polymer solution for spin-coating was
prepared by dissolving the polymer (1 wt%) in chlorobenzene. Ca
and aluminium contacts were formed by vacuum deposition at
pressures below 10ꢂ6 Torr, giving an active area of 0.04 cm2.
Materials
Synthesis of 2-{2,6-bis[2-(7-bromo-10-hexyl-10H-phenothiazin-
3-yl)vinyl]pyran-4-ylidene}malononitrile (bis-PTZDCM) (3). A
solution of (2,6-dimethyl-4H-pyran-4-ylidene)malononitrile
Phenothiazine, N-bromosuccinimide (NBS), phosphorus oxy-
chloride, 1,1,2-trichloroethane, tetraethylammonium hydroxide
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(0.94 g, 5.5 mmol), 2 (4.68 g, 12 mmol), piperidine (0.6 ml) and
n-propanol (30 ml) was refluxed for 1 day. After completing the
reaction, the reactant was cooled to room temperature and excess
methanol was added to obtain a red solid. Then reprecipitation
in methanol/methylene chloride yielded the red solid of 3 (3.43 g,
0.97–0.60 (b, 10H). Anal. Calcd: C, 89.62; H, 10.37; N, 0.0074; S,
0.0085. Found: C, 89.60; H, 10.36; N, 0.015%.
Acknowledgements
1
68%). H NMR (400 MHz, DMSO-d6, ppm): d 7.65 (m, 6H),
This work was supported by BK21 of the Ministry of Education
and Human Resources Development and Dongjin Semichem.
Co.
7.37 (m, 4H), 7.24 (d, 2H), 7.09 (d, 2H), 6.98 (d, 2H), 6.79 (s, 2H),
3.89 (t, 4H), 1.66 (q, 4H), 1.38 (m, 4H), 1.25 (m, 8H) 0.83 (t, 6H).
13C NMR (100 MHz, DMSO-d6, ppm): d 159.3, 156.0, 149.4,
149.2, 141.9, 134.7, 130.9, 130.3, 130.0, 129.3, 127.9, 125.1, 123.3,
118.1, 116.4, 115.5, 114.3, 56.1, 47.0, 30.9, 25.9, 25.6, 21.9, 13.8.
Anal. Calcd for C48H44Br2N4OS2: C, 62.88; H, 4.84; N, 6.11; S,
6.99. Found: C, 63.05; H, 4.86; N, 6.19; S, 6.81%.
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representative example. 2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)-9,90-di-n-octylfluorene (0.450 g, 0.70 mmol),
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F8R8 was synthesized with the procedure described for F8R5.
The copolymerization of the monomers 2,7-bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-9,90-di-n-octylfluorene (0.450 g,
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(b, 4H), 2.28–1.81 (b, 4H), 1.28–0.97 (b, 20H), 0.97–0.60
(b, 10H). Anal. Calcd: C, 89.62; H, 10.37; N, 0.0059; S, 0.0068.
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This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 7062–7069 | 7069